First of all, I must watch your art-style to give you an answer but:
Maybe the best way to animate this kinds of objects is using a sprite animation. Make 5 or 6 sprites with the movement, insert them into a slot, and switch the sprites each frame.
It isn't a easy way for that kinds animations i think.
Maybe if your art-style its simple you could use 2 bones or 3 to make a little wave effect on the cloak.
If you can, put a example of a character.